SQUARE D
SQUARE D QOB140 Miniature Circuit Breaker 40A 1 Pole 120/240V AC
Protects single-phase 120/240 V AC circuits up to 40 A with a 10 kA interrupt rating in a bolt-on QO frame
- 40 A single-pole protection for 120/240 V AC circuits
- 10 kA interrupting rating handles high fault currents
- Bolt-on mounting fits Square D QO load centres
- 48 V DC rating adds low-voltage versatility
- Compact 3.1 × .8 × 2.9 in frame saves panel space
Square D QOB140 40 A bolt-on breaker
The Square D QOB140 is a single-pole miniature circuit breaker rated at 40 A and 120/240 V AC. It uses the QO bolt-on mounting style and fits Square D NQOD panelboards. The device carries a 10 kA interrupting rating at the rated voltage. It also supports 48 V DC circuits.
Thermals noise and power draw
The breaker operates within a minimum temperature of 77 °F. As a passive protection device it generates no audible noise and draws no operating power. Thermal-tripping action responds to sustained over-current without external energy. The paddle actuator provides manual switching.
Deciding specification
The bolt-on QO mounting style is the single specification that determines compatibility. Only panelboards designed for QO bolt-on breakers will accept this unit. Buyers with plug-on or DIN-rail panels cannot use it.
Highlights
- 40 A single-pole protection for 120/240 V AC circuits
- 10 kA interrupting rating handles high fault currents
- Bolt-on mounting fits Square D QO load centres
- 48 V DC rating adds low-voltage versatility
- Compact 3.1 × .8 × 2.9 in frame saves panel space
Specifications
| Brand | SQUARE D |
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Questions about this item
How do I bolt this QOB140 breaker onto the panel rail, and what step is often missed?
Align the bolt-on foot with the QO panel rail, tighten the mounting screw securely, then snap the paddle actuator down until it locks; the step often missed is fully tightening the mounting screw before energising the panel.
What maintenance or replacement will this 40 A single-pole breaker need over time?
Periodically torque the lug terminal to the manufacturer value, exercise the paddle actuator annually, and replace the breaker if it trips at or below 40 A during a calibrated test or shows discoloration at the lug.
What limit appears first when this breaker runs continuously near 40 A in a 77 °F ambient?
The thermal element will reach its trip curve first; sustained current at 40 A in 77 °F ambient causes the breaker to open on its inverse-time characteristic before the 10 kA interrupting rating or 120/240 V AC voltage rating becomes a factor.
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